Soil sterilizer



Oct. 14, 1958 I. w. DILLON 2,856,505

SOIL STERILIZER Filed Feb. 21, 1957 70 O0 O0 00 Q 0 '0 0 6/ 45 0-0 0-0 Q0 0 o a 0 7/ United This invention relates to apparatus for sterilizing batches of soil by the use of electrically produced heat, and more particularly to improvements in the soil sterilizing apparatus described and claimed in my application, Serial No. 348,955, filed April 15, 1953, now Pat. No. 2,784,286. According to the present invention, the heating plates are arranged for a more uniform distribution of heat through the mass of earth in the device, provision is made for a supply. of moisture to promote the penetration of heat to all parts of the earth mass, and safety devices are included to avoid excessive wetting and local overheating but to ensure sufiicient heating of the entire contents of the container. For this purpose the heating plates are each provided with a water duct and a heating unit, the latter serving to vaporize water in the duct as well as to heat the plate. One of the plates is provided with a thermostat which operates to cut oflf the electric current from the heating units in the several'plates when the temperature at the thermostat exceeds a predetermined degree. When the current is thus shut off, a control valve in the water supply line to the ducts is automatically opened. The vaporization of some of the water cools the plates sufficiently to cause the thermostat to turn the current on again andto shut the water valve.

Soil sterilizers are usually used in greenhouses where the attendants have various duties and cannot give much attention to the sterilizer after it has been put into operation. An object of the present invention is to avoid undesirable consequences which might otherwise result from such inattention.

For a more complete understanding of the invention reference may be had to the following description thereof and to the drawing, of which- Figure l is a perspective view of an apparatus embodying the invention, portions of the covers and front wall being broken away;

Figure 2 is a fragmentary plan view of the same, part of the covers being broken away;

Figure 3 is a section on the line 33 of Figure 4;

Figure 4 is a section on the line 4-4 of Figure 2;

Figure 5 is a rear elevation of the apparatus with the rear outer casing removed;

Figure 6 is a front elevation on a larger scale, of one of the heating plates;

Figure 7 is a side elevation, on a larger scale, of one of the support brackets for the rear end of the heating plate;

Figure 8 is an end elevation of the bracket shown in Figure 7;

Figure 9 is an enlarged fragmentary elevation of the piping shown in Figure 5, a portion being broken away to show interior structure; and

Figure 10 is an enlarged fragmentary plan view of part of the piping shown in Figure 5, a portion being broken away to show interior structure.

The embodiment of the invention illustrated on the tates Patent O 2 drawing comprises a rectangular box having side walls 20 and 22, end walls 24 and 26, and a two-part bottom, the parts 28 and 30 being flaps which are hinged to the end walls 24, 26 respectively. When the bottom is closed so that the box can be filled with earth, the flaps 28 and 30 are held in the closed position shown -in Figure 4 by suitable latches 32 and 34 which are connected by a shaft 35 so that they act together to support or release the free edges of the flaps. The box may be supported by suitable legs 36 at the corners, the legs being long enough to permit the flaps 28 and 30 to swing down to the vertical position without hitting the floor on which the legs stand. Within the box are mounted a number of heating plates 40 arranged in parallel vertical planes, these plates extending from near the end wall 24 to near the end wall 26. The plates are relatively thin but are reinforced by a top bulb or rib 42 extending along the upper edge thereof, vertical ribs 44 spaced at intervals along the plate, and two en largements 46 and 48 which are tubular and which extend horizontally from one end of each plate to the other. These enlargements also project beyond both ends of the plate so that the plate can be supported thereby. The upper tubular enlargement 46 of each plate is closed at one end and is provided with a series of small perforations 50 through the wall thereof, the purpose of this perforated enlargement being to supply moisture in the form of vapor for the purpose of more rapidly disseminating heat through the earth which is to be sterilized. The tubular enlargements 46 are connected to a simple piping system 52 indicated in Figure 5, the pipe running to a reservoir 54 which holds a limited supply of water. This prevents excessive flooding of the box and the floor on which it stands which might otherwise result from inattention. A shutoff valve 56 is supplied in the pipe line to turn the water on and off. As it is desirable that the moisture supplied to the earth through the perforations 50 be in the form of vapor, an electrically operated valve is preferably employed, this valve being thermostatically controlled as hereinafter described. Within the pipe 52 near the valve 56 is a constriction 57 in the form of a diaphragm through which a small hole has been drilled. This limits the flow of water from the reservoir to the perforated enlargements 46 to a quantity that can be vaporized completely when the plates are heated to their prescribed maximum temperature.

To avoid uneven distribution of the water to the several plates, the T-fittings 58 which connect the enlargements 46 to the supply pipe 52 are furnished with diaphragms 59 which are drilled to provide a hole smaller than the hole in the diaphragm 57.

Each lower horizontal enlargement 48 of the plates 40 contains an elongated electric heating unit. These units have terminal wires projecting beyond the ends of the enlargements 48, the terminals being connected as indicated in Figures 3 and 5. The heating units are thermostatically controlled as follows. Lead lines L from a power supply enter through a control switch 60. A wire 61 and a return wire 62 connect the switch 60 to a relay 63. A thermal cut-off device 64 and a thermostat 65 are connected in series with the relay 63, the arrangement being such that if either of these devices breaks the circuit, the relay opens the circuit through the heating units in the enlargements 48. The heating units are connected in series-parallel, a lead wire 66 running from the relay 63 to near ends of two of the four units. At the far end of the box the terminals of these two units are connected respectively by wires 68 to the far ends of the other two heating units (Figure 5). The near ends of these other two units are connected by a return wire 70 to the switch 60.

The thermostat 65 is housed in one of the heating plates 4t) near the lower edge thereof as indicated in Figure 4. Whenever it reaches a predetermined maximum temperature, it operates to cut off the electric power from the heating units until it cools to a lower temperature for which it has been set to switch the current on again. The thermostat as is also connected in series with the solenoid-operated valve 56 in a branch circuit including connecting wires 71. and 72. The connections are such that the valve 56 is normally shut. When the thermostat heats up to the temperature at which it is set to act, it simultaneously cuts oil the current to the heating units in the plates 4t? and opens the valve 56. Since by that time the plates themselves, and especially the enlargements 46 thereof, have been heated up to approximately the same temperature as the thermostat 65, the Water that trickles into the enlargements 46 is vaporized and discharged through the perforations 50 into the soil, it being assumed that the soil is sulficiently dry and open to be full of interstices through which vapor can penetrate. The vapor condenses in the cooler soil but as the quantity rate of delivery is limited, the condensate is not sufficient to soak the soil. it the soil is soaked, the interstices therein are Water-sealed and the penetration of vapor therethrough is stopped.

It is desirable that all of the soil in the box be sufficiently heated. For this purpose the thermal cut-ofi 64 is located in a lower corner of the box as indicated in Figures 3 and 4-. When the soil adjacent to this thermal cut-off has reached the temperature required for a thorough sterilization, it is assumed that all the rest of the soil in the box has by that time been sterilized. The thermal cut-off 64 thereupon acts to break the circuits and stop further heating and water flow until it has been manually reset for the treatment of another batch of earth.

To facilitate the removal of individual plates from the box, the ends of the plates which are adjacent to the end wall 26 are supported by thimbles 74 such as are shown in Figures 7 and 8. In order to remove a plate 40 from the box the pipe 52 is disconnected, the electrical connections are disconnected, the thimbles are withdrawn from the wall 26, and the plate can then be lifted out.

The pipe connections and electrical connections may be protected by being enclosed in compartments 75 and 76 adjacent to the end walls 24 and 26 respectively. The compartment 75 has an outer wall 77 and a permanent cover 78. In like manner the compartment 76 has an outer wall 80 and a permanent cover 32. A loose cover 84 is provided for the box 20. This cover fits inside of the end walls and side walls of the box and rests on the earth which is heaped in the box.

When it is desired to sterilize a batch of earth, the bottom flaps 28 and 30 are secured in their closed position. The box 20 is then filled with the earth to be sterilised and the cover 84 is put in place. The reservoir 54 is filled with water, the valve 56 being closed. The electric current is turned on so that the plates heat up until the thermostat 65 reaches the temperature at which it has been set to operate. The thermostat then operates to turn off the heating current and turn on the water valve 56. Water trickles into the enlargements 46 of the plates as which are then hot. The water is vaporized, lowering the temperature of the plates until the thermostat acts to turn on the current through the heating units and to turn off the water valve. This onand-ott operation of the thermostat continues until the heat has penetrated through the entire mass of earth sufiiciently to raise the temperature of all of it to the required degree. The thermal cut-oil 66 then operates automatically to open the circuits. The bottom flaps 28 and 3t) can then be manually released to allow the charge of earth to fall on to the floor which supports the box. The legs 36 prevent the flaps from swinging beyond the vertical position so that the pile of earth which falls from the box cannot spread beyond the ends of the box. When the sterilized earth has been scooped up and removed, the bottom flaps are swung to their closed position and secured there by the latches 32, and the thermal cut-off is reset. The box is then ready to receive the next batch of earth to be sterilized.

Boxes for soil sterilization are made in various sizes. Ey way of example, the dimensions of the box 2d may be 36" x 36 x 18', the plates 40 being 9 apart. The reservoir 54 for this box may have a capacity of five quarts. The pin-hole in the diaphragm 57 may be 0.45 while that in the diaphragms 59 may be 0.30". The thermostat as may be set to operate at 250 F. to turn the current off and at 245 F. to turn it on again. The thermal cut-oh 64 may be set to terminate the operation of the apparatus when it is heated to F. It is to be understood that the foregoing figures are by Way of illustration only, and not limitation, and that the invention includes such variations and modifications as may be within the scope of the appended claims.

I claim:

1. Apparatus for sterilizing soil, comprising a box having two pairs of opposed walls and a bottom, a series of heating plates mounted in said box in spaced parallel planes, each said plate having two horizontal tubular enlargements extending from end to end of the plate and projecting beyond the ends to the adjacent walls of the box, an electric heating unit disposed in the lower of said enlargements of each said plate, means for connecting the electric heating units in the plates to a source of power, the upper enlargement of each said plate having small perforations spaced along its length, and water connections for the perforated enlargements.

2. Apparatus for sterilizing soil, comprising box hav ing two pairs of opposed walls and a bottom, said bottom comprising two parts hinged respectively to opposed walls, means releasably fastening said bottom parts in horizontal position, a series of heating plates mounted in said box in spaced parallel planes, an elongated horizontal electric heating unit housed in each said plate, an elongated perforated duct in each said plate above said heating unit, means for connecting said heating units to a source of power, water supply pipe connections for said ducts, and a cover for said box. 3. Apparatus as in claim 1, a reservoir mounted adacent to said box and communicating with said water connections, a normally closed shut-off valve in said water connections, thermostatic means responsive to the heating of one of said plates to open said valve, and a constriction in said water connections between the reservoir and the perforated enlargements to limit the rate of flow of liquid to the perforated enlargements.

4. Apparatus as in claim 1, a thermostat embedded in one of said plates and connected into the circuit with said heating elements to control the same, and a thermal cutoff device located at the bottom of said box adjacent to an end wall thereof and connected into said circuit.

5. Apparatus for sterilizing soil, comprising a box side walls, end walls and a bottom, a series of heating plates arranged in spaced parallel planes and extending between and supported by said end walls, each said plate having upper and lower horizontal tubular enlargements extending from end to end thereof and beyond the ends to said end Walls, said upper enlargements each having a series of small perforations therethrough, said lower enlargements each having an electric heating unit therein, a reservoir mounted adjacent to said box, water connections from said reservoir to an end of each of said upper enlargements, a constriction in said water connections to limit the flow of water to said perforated enlargements, means for connecting said heating elements to a source of electric power, and a removable cover on said box.

6. Apparatus for sterilizing soil, comprising a box having four walls, a series of heating plates mounted in parallel vertical planes in said box and supported by certain of said walls, each said plate having two tubular enlargements one of which is provided with a series of spaced perforations, an electrical heating unit in the other enlargement of each said plate; a reservoir mounted above said box, a supply pipe leading from said reservoir, branch pipes connecting said supply pipe to said perforated enlargements, a diaphragm in said supply pipe having a small hole therethrough to restrict the flow of water from said reservoir, and a diaphragm in each said branch pipe having a smaller hole therethrough.

7. Apparatus for sterilizing soil, comprising a box having four walls, a series of heating plates mounted in parallel vertical planes in said box and supported by certain of said walls, each said plate having two tubular enlargements one of which is provided with a series of spaced perforations, an electrical heating unit in the other enlargement of each said plate, water connections to said perforated enlargements, means in said connections limiting the rate of flow of water to each said plate, electric connections for said heating units, an electrically operated shut-off valve in said water connections, and thermostatic means for opening the circuits to said heating units and opening said valve when the temperature of one of said plates exceeds a predetermined degree.

8. Apparatus as in claim 7, and a thermal cut-off device located in said box and connected in said circuits to make a break in the same when the device exceeds a predetermined temperature, said device having manually operable means to close said break.

Parsons Apr. 2, 1935 Lord Nov. 28, 1944 

